Projection exposure system having a reflective reticle

ABSTRACT

A projection exposure system for microlithography includes an illuminating system ( 2 ), a reflective reticle ( 5 ) and reduction objectives ( 71, 72 ). In the reduction objective ( 71, 72 ), a first beam splitter cube ( 3 ) is provided which superposes the illuminating beam path ( 100 ) and the imaging beam path ( 200 ). In order to obtain an almost telecentric entry at the reticle, optical elements ( 71 ) are provided between beam splitter cube ( 3 ) and the reflective reticle ( 5 ). Advantageously, the reduction objective is a catadioptric objective having a beam splitter cube ( 3 ) whose fourth unused side can be used for coupling in light. The illuminating beam path ( 100 ) can also be coupled in with a non-parallel beam splitter plate. The illuminating beam path is refractively corrected in passthrough to compensate for aberrations via the special configuration of the rear side of the beam splitter plate. Advantageously, a beam splitter plate of this kind is used within a reduction objective in lieu of a deflecting mirror and only refractive components are introduced between the beam splitter plate and the reflective reticle.

FIELD OF THE INVENTION

The invention relates to a projection exposure system having a reticlewhich operates in reflection.

BACKGROUND OF THE INVENTION

Projection exposure systems having a reflective reticle have been usedin the past, inter alia, together with 1:1 Dyson objectives. Theseprojection exposure systems are described in the following publications:

-   a) Owen et al, “⅛ μm optical lithography” J. Vac. Sci. B 10 (1992),    pages 3032 to 3036, especially Parts B and C;-   b) Pease et al, “Lithography for 0.25 μm and below . . . ” IEEE    Symp. VLSI Technology (1992), pages 116 and 117;-   c) Jeong et al, “Optical projection system . . . ” J. Vac. Sci. B 11    (1993), pages 2675 to 2679; and,-   d) U.S. Pat. No. 4,964,705.

The incoupling of the illumination takes place via a partiallytransmitting mirror as shown, for example, in U.S. Pat. No. 4,964,705(FIGS. 3A and 3B). Beam splitter cubes or beam splitter plates are notprovided in these designs.

Reflective reticles are used exclusively in the area of lithographyutilizing soft X-rays (EUVL). The beam splitting of illuminating andimaging beam paths is realized by an inclined incidence of theillumination. Beam splitter cubes or beam splitter plates are not used.The objectives are pure mirror objectives having a non-axial symmetricalbeam path. The inclined incidence of the illuminating light on thereflective reticle has the disadvantage that the raised mask struts leadto vignetting.

Japanese patent publication 9-017719 discloses a wafer projectionexposure system having a reflex LCD as a special reticle. According toFIG. 1 of this publication, a planar beam splitter plate is used toseparate the illuminating and imaging beam paths. Illuminating systemand projection objective are operated with a field symmetrical to theoptical axis. The incoupling of the illuminating light via a beamsplitter plate directly ahead of the reticle as shown in Japanese patentpublication 9-017719 requires, on the one hand, the corresponding entryintersection distance, and, on the other hand, the passthrough throughthe planar plate leads to the astigmatic deformation of the illuminatinglight between which disturbs the required clean pupil imaging.

U.S. Pat. No. 5,956,174 discloses a catadioptric microscope objectivewherein the illuminating light is coupled in via a beam splitter cubebetween the microscope objective and the tube lens. This type ofillumination is conventional in reflected light microscopes. Theilluminating field sizes are only in the order of magnitude of 0.5 mm.

Catadioptric systems for wavelengths of 193 nm and 157 nm are known.Catadioptric projection objectives having beam splitter cubes without anintermediate image are shown, for example, in U.S. Pat. Nos. 5,742,436and 5,880,891 incorporated herein by reference.

Catadioptric projection objectives having a beam splitter cube and anintermediate image are disclosed in U.S. Pat. No. 06/424,471 6,424,471.

Illuminating devices for microlithography are disclosed in U.S. Pat. No.5,675,401 and U.S. Pat. No. 6,285,443. So-called REMA objectives forimaging a reticle masking device (REMA) into the plane of the reticleare disclosed in U.S. Pat. No. 5,982,558 and U.S. Pat. No. 6,366,410,also incorporated herein by reference. With these objectives, interalia, the entry pupil of the downstream projection objective isilluminated.

The production of transmission reticles (that is, masks operated intransmission for microlithography) is difficult for deep ultravioletwavelengths, especially 157 nm, inter alia, because of suitabletransmitting carrier materials. The materials CaF₂ or MgF₂ can beconsidered. However, reticles made of CaF₂ or MgF₂ are difficult toprocess and are therefore very expensive. Furthermore, a reduction ofthe minimal structural size which can be applied to a semiconductor chipresults because of absorption and the thermal expansion of the reticleresulting therefrom when there are multiple illuminations. Whenpossible, materials such as MgF₂ are avoided because they are alsodouble refracting.

The alternative are reflective reticles. To reduce the requirementsimposed on the reticle, it is advantageous when the projection objectiveis configured as a reduction objective and the reticle is imaged so asto be demagnified. The reticle can then be provided with largerstructures.

In conventional reduction objectives, the use of reflective reticles isnot easily possible. The typical entry intersection distance of, forexample, 30 mm reduces the illumination at suitable angles of incidence.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a projection exposure systemhaving a reduction objective which functions without problem withreflective reticles.

The projection exposure system of the invention is for microlithographyand includes: a light source; an illuminating system mounted downstreamof the light source for transmitting light from the light source as anilluminating beam along an illuminating beam path; a reflective reticle;a reduction objective defining an imaging beam path and being configuredfor imaging the reticle onto an object; and, a beam splitter cubemounted in the imaging beam path for mutually superposing theilluminating beam path and the imaging beam path.

According to a feature of the invention, a beam splitter cube functionsto superpose the illuminating and imaging beam paths. In this way,numerous objective design concepts for reflective reticles can beadapted as will be shown in the following examples. Erroneous entries bythe beam splitter plate are avoided by utilizing a beam splitter cube inlieu of a planar parallel beam splitter plate. The beam splitter plateis operated in passthrough and mounted at 45°.

According to another feature of the invention, optical elements areprovided between the beam splitter cube and the reticle. With theseoptic elements, it is possible to reduce the angle of incidence of themain beams of the reduction objective on the reticle in such a mannerthat the incident angle has values between −15 mrad and +15 mrad.

According to still another feature of the invention, the illuminatingsystem is so configured that the illuminating beam path passes over intothe imaging beam path with deviations of less than ±2.5 mrad. Thisdeviation can be measured in that the angles with respect to the reticleplane are determined for the centroidal rays after the reflection andthe deviation to the angles of the corresponding chief rays is computed.The angles of the centroidal rays are dependent upon the emissioncharacteristics of the light source and the design of illuminatingsystem and the angles of the chief ray are exclusively dependent uponthe design of the reduction objective.

According to another feature of the invention, a polarization beamsplitter cube is used in order to reduce transmission losses at the beamsplitter cube and so that no scattering light is deflected onto thewafer. For an optimal operation, the illuminating light should belinearly polarized to more than 95%. The polarization direction isdependent upon whether the illuminating beam path is intended to bereflected or not at the beam splitter layer. In the case of areflection, the illuminating light has to be polarized parallel to thebeam splitter surface and, in the case of the transmission, theilluminating light has to be polarized perpendicularly to the beamsplitter surface.

In other embodiments of the invention, the beam splitter cube functionsexclusively for incoupling the illuminating beam path. To be able tomore easily integrate the beam splitter cube into the design of thereduction objective, it is advantageous to subdivide the reductionobjective into two component objectives with a first intermediate imagehaving an imaging scale of −1.0±0.25 and a second image having animaging scale of −0.25±0.15. The beam splitter cube is integrated intothe first intermediate image. The second image can be configured to bestrictly refractive or catadioptric.

The coupling in of the illuminating beam path with a beam splitter cubeis especially advantageous when the beam splitter cube is already a partof the reduction objective. Then, the fourth unused face of the beamsplitter cube can be used to couple in the illuminating beam path.

If the design of the catadioptric objective includes a deflectingmirror, then the deflecting mirror can be replaced by a beam splittercube via which the illuminating light is coupled in.

The design of the catadioptric objective can be configured with orwithout an intermediate image.

In another embodiment of the invention, a special beam splitter plate isprovided in the projection exposure system. This beam splitter plate isoperated in pass through in the illuminating beam path and is operatedreflectively in the imaging beam path. Here, reflection in air isprovided, that is, in the optically thinner medium which can also be avacuum or a special gas mixture or a gas such as nitrogen or helium. Thebeam splitter plate is so configured that astigmatic errors because ofthe plate mounted at an angle can be refractively corrected.

The common inventive concept is that the imaging beam path is held freeof disturbances by the beam splitter arrangement and the illuminatingbeam path is corrected with less requirements directly via the beamsplitter arrangement. For a beam splitter cube, onlyrotationally-symmetrical imaging errors are introduced which can becorrected within the illuminating system via rotationally-symmetricaloptical elements such as spherical lenses. In the beam splitter plateaccording to a feature of the invention, the correction of theilluminating beam path is provided by the special configuration of theside of the beam splitter plate facing toward the illuminating system.

According to still another feature of the invention, the beam splitterplate is provided with a non-planar corrective surface. By mounting thebeam splitter plate at an angle, the corrective surface exhibits norotational symmetry, rather, a simple symmetry with respect to themeridian plane.

The beam splitter plate is configured to have a wedge shape inaccordance with another embodiment of the invention for correcting theastigmatism of the lowest order. The use of a beam splitter plate isespecially advantageous when it is used in lieu of a deflecting mirrorprovided in the design of the reduction objective.

The superposition of the illuminating optics and the projection opticsmake possible the use of reflective reticles especially at operatingwavelengths in the range from 100 to 200 nm. In this way, thedifficulties are avoided which occur in the manufacture of transmissionreticles because of machining of the materials transparent at thesewavelengths.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be explained with reference to the drawingswherein:

FIG. 1 is a schematic of a reduction objective having a reflectivereticle and a beam splitter cube for coupling in the illumination light;

FIG. 2 shows a reduction objective with an intermediate imaging opticdisposed ahead of the reduction objective and with a beam splitter cubebeing integrated for coupling in illumination;

FIG. 3 shows a catadioptric reduction objective having an intermediateimaging optic disposed forward thereof into which the beam splitter cubeis integrated for coupling in illumination;

FIG. 4 shows a catadioptric reduction objective without an intermediateimaging optic wherein the illuminating beam path is coupled in via thebeam splitter cube of the catadioptric reduction objective;

FIG. 5 shows a catadioptric reduction objective without an intermediateimaging optic where the illumination is coupled in via a beam splitterplate at the location of the deflection;

FIG. 6 shows a catadioptric reduction objective without an intermediateimaging optic wherein the illumination is coupled in via a beam splittercube at the location of the deflection;

FIG. 7 shows a catadioptric reduction objective having an intermediateimaging optic wherein the illumination is coupled in via the beamsplitter cube of the catadioptric reduction objective; and,

FIG. 8 shows an embodiment for a catadioptric reduction objective havinga beam splitter cube and an intermediate imaging optic.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 1 shows a typical configuration of a projection exposure system formicrolithography in accordance with an embodiment of the invention. Thereflective reticle 5 is imaged via demagnifying imaging optics onto thewafer 6 at a typical imaging scale β of −0.25±0.15. The illuminatedfield on the wafer 6 has a diameter of at least 10 mm. Rectangularfields having an x-y aspect ratio of 1:1 to 1:4 are typical. The imageend numerical aperture is greater than 0.5. The imaging takes place viathe optical elements 71 and 72. A beam splitter cube 3 is integratedinto the imaging beam path 200 of the reduction objective betweenreflective reticle 5 and wafer 6 for illuminating the reflective reticle5. The beam splitter cube can, for example, be a polarization beamsplitter cube wherein a layer system is located between the prismsurfaces. This layer system almost completely reflects polarized lightparallel to the beam splitter surface 30; however, the beam splittersurface 30 is light transmissive for polarized light perpendicular tothe beam splitter surface 30.

A condition precedent for the arrangement of FIG. 1 is therefore thatthe illuminating light is polarized in parallel to the incidence planeof the beam splitter surface 30 mounted at an angle of 45°. Polarizedlight of this kind is reflected at the beam splitter surface 30 and isdeflected in the direction of reflective reticle 5. A λ/4 plate 4 ismounted between the beam splitter cube 3 and the reflective reticle 5and this plate 4 is run through a total of two times. The first time isin the illuminating beam path 100 so that the linearly polarized lightis polarized circularly. After the reflection at the reticle 5, thecircularly polarized light in the imaging beam path 200 runs the secondtime through the λ/4 platelet 4 and is now again linearly polarized. Thepolarization direction now, however, is aligned perpendicular to thebeam splitter surface 30 of the beam splitter cube 3 so that the beamsplitter cube 3 is passed through without reflection. In this way, aseparation of the illuminating light beam path 100 and of the imagingbeam path 200 is provided in the combination of the following:polarization beam splitter cube 3, two-time passthrough of the λ/4platelet 4 and the reflective reticle 5. A plane-parallel beam splitterplate would have the disadvantage compared to the polarization beamsplitter cube 3 that rotationally-symmetrical imaging errors would notbe introduced by the beam splitter plate of finite thickness positionedat an angle of 45°.

The polarization beam splitter cube 3 should be mounted within theimaging beam path 200 at a location at which the rays impinging on thebeam splitter surface 30 exhibit a slight divergence. This is the casewhen the polarization beam splitter cube 3 is disposed at a locationhaving an almost collimated beam path. For this reason, optical elements71 having an overall positive refractive power are to be providedbetween reflective reticle 5 and the polarization beam splitter cube 3.The optical elements 71 essentially collimate the diverging beam comingfrom the reticle. The optical elements 72 can, in accordance with thetype of design, be configured differently but also likewise have apositive refractive power in order to achieve imaging on a possibleintermediate image plane or on the wafer plane 6.

One can view the optical elements 71 and 72 taken together as arefractive reduction objective having a typical imaging scale β of−0.25±0.15. In the design of the refractive objective, the λ/4 platelet4 and the beam splitter cube 3 are to be provided between the opticalelements 71 and the optical elements 72.

The reflective reticle 5 is illuminated with the aid of the illuminatingsystem 2. In the design of the illuminating system 2, the beam splittercube 3, the λ/4 platelet 4 and the optical elements 71 need beconsidered. The interface between the illuminating system 2 and theimaging optic is therefore not the reticle 5 as would be the case in atransmission reticle or when there is an inclined illumination of thereticle; instead, the interface is the input of the beam splitter cube 3facing toward the illuminating system 2.

In order to simplify the optical configuration of the illuminatingoptics 2, it is advantageous when the chief ray angles are less than ±15mrad with reference to the reticle plane, that is, the reticle 5 isvirtually telecentrically illuminated. The chief rays are so defined inthe reduction objective that they intersect the optical axis at thelocation of the system diaphragm. For larger chief ray angles, thedesign of the illuminating optics 2 is thereby made more difficultbecause the centroidal rays of the illuminating beam path 100 have topass in the reticle plane 5 into the chief rays of the imaging beam path200. Because of the reflection at the reticle, the incident angles ofthe centroidal rays have to exhibit the reverse sign from the incidentangles of the chief rays. In this way, the illuminating beam path 100 isdifferent from the imaging beam path 200 within the optical components71. The distribution of the chief ray angles over the illuminated fieldhas to be overcompensated by the illuminating system 2. The chief rayangle distribution at the reticle 5 is determined primarily by theoptical elements 71 and these optical elements 71 are fixedly pregivenfor the design of the illuminating system 2. For these reasons, opticalcomponents have to be provided in the illuminating system 2, such as asequence of converging and diverging lenses, which operate on thecentroidal ray angle on the reticle 5.

The optical components in the illuminating system 2 are so configuredthat the centroidal rays of the illuminating beam path 100, after thereflection at the reflective reticle 5, are coincident with the chiefrays up to a maximum angle deviation of ±2.5 mrad depending upon fieldheight. The chief rays are pregiven by the design of the reductionobjective. Otherwise, the usually required telecentricity in the waferplane 6 is deteriorated.

The illuminating system 2 has to have a unit for changing thepolarization state of the illuminating light. In linearly polarizedlight of the source 1, the polarization direction has to be rotated, asrequired, for example, via double refracting crystals or doublerefracting foils. For unpolarized light of the source 1, polarizers areused for generating light which is polarized perpendicularly orparallely to the beam splitter surface 30. Preferably, these componentsfor influencing the state of polarization are introduced directlyforward of the polarization beam splitter cube 3. The polarizationdirection is dependent upon whether or not the illuminating beam path100 should be reflected at the beam splitter layer 30. In the case of areflection, for example, the illuminating light has to be polarizedparallel to the beam splitter surface 30.

Conventionally, the illuminating system 2 includes integrators forhomogeneously illuminating the reticle plane 5. The integrators are, forexample, honeycomb condensers, hollow conductors or glass rods. Forvarying the illumination mode, the illuminating system can include: twozoom optics, axicon elements, filter plates in the pupillary planesand/or masking devices in the pupillary field planes or in theintermediate field planes.

The operation of these elements is disclosed, for example, in U.S. Pat.No. 6,285,443, and incorporated herein by reference. Objectives withinthe illuminating system 2 for adapting the centroidal ray angles of theilluminating beam path 100 to the chief ray angles of the reductionobjective are known as REMA objectives for the correct illumination ofthe entry pupil of the reduction objective from U.S. Pat. No. 6,366,410and from U.S. Pat. No. 5,982,558, both incorporated herein by reference.

As a light source, a DUV laser or VUV laser can be used, for example, anArF laser at 193 nm, a F₂ laser at 157 nm, an Ar₂ laser at 126 nm and aNeF laser at 109 nm.

FIG. 2 shows a further embodiment of the projection exposure system ofthe invention for microlithography. Components in FIG. 2 whichcorrespond to those in FIG. 1 are identified with the same referencenumerals. The imaging system (7, 8) in FIG. 2 includes an intermediateimage plate 103. The intermediate imaging system 7 includes the opticalelements 101, the λ/4 platelet 4, the polarization beam splitter cube 3and the optical elements 102. The intermediate imaging system 7 thenprovides an intermediate imaging of the reflective reticle 5 onto theintermediate image plane 103. The imaging scale β₁ of this intermediateimaging can, for example, be β₁=−1.0±0.2. Also possible is a reductionimaging at an imaging scale, β₁=−0.5±0.2 if thereby the design of thedownstream optical system 8 is simplified. In this case, the incouplingof the illuminating light takes place via the polarization beam splittercube 3 with the downstream λ/4 platelet 4 within the intermediateimaging optics 7. The optical elements 101 and 102 each have a positiverefractive power. The polarization beam splitter cube 3 is disposed in aregion having an almost collimated beam path. Optical elements 104follow the intermediate image plane 103 and image the intermediate imageplane 103 onto the wafer plane 6 at an imaging scale of B₂=−0.25±0.15 orβ₂=0.5±0.15. In this embodiment, the reduction objective is subdividedinto the intermediate imaging system 7 and the reduction system 8. Thisaffords the advantage that, in the intermediate imaging system 7,adequate space is provided for the polarization beam splitter cube 3.Also in this configuration, the optical elements 101, the λ/4 platelet 4and the beam splitter cube 3 are included in the design of theilluminating system 2. It is advantageous when the intermediate imagingoptics 7 are so configured that the reflective reticle 5 is almostentirely telecentrically illuminated. The angles of incidence of thechief rays on the reflective reticle 5 should then be less than 15 mrad.

FIG. 3 shows an additional embodiment of the projection exposure systemof the invention for microlithography. The imaging between reflectivereticle 5 and wafer plane 6 takes place with two intermediate imageplanes 113 and 118. The intermediate imaging system 9 of reflectingreticle 5 to intermediate image plane 113 is configured similarly to theintermediate imaging system 7 of FIG. 2. The imaging of intermediateimage plane 113 on the wafer 6 takes place first with the aid of thecatadioptric intermediate imaging system 10 and a downstream refractivereduction system 11. The catadioptric intermediate imaging system 10comprises the optical elements 114, a deflecting mirror 115, the opticalelements 116 and the concave mirror 117. The object field of theintermediate imaging system 10 is not centered with respect to theoptical axis because of the reflective deflecting mirror 115; instead,the object field is outside of the optical axis. This means in this casethat the component systems 10 and 11 must be arranged offset to thecomponent system 9. For these projection objectives, the image endnumerical aperture can have values in the range from 0.65 to 0.8 ormore. Field sizes in the wafer plane 6 in the range from 20 mm×7 mm to30 mm×10 mm are possible. Objectives of this kind are disclosed in U.S.Pat. No. 6,496,306, and incorporated herein by reference.

The incoupling of the illuminating beam path 100 into the imaging beampath 200 can be done in an especially advantageous manner when a beamsplitter cube is already provided in the imaging beam path 200 as is thecase in some catadioptric objective types. Catadioptric objective typeshaving beam splitter cubes are known in various configurations.

FIG. 4 shows a possible catadioptric projection objective having a beamsplitter cube 31 which is assembled without an intermediate image.Objectives of this kind comprise, starting with the reticle 5: a firstlens group 121, a deflecting mirror 122, a second lens group 123, thebeam splitter cube 31, a third lens group 124, a concave mirror 125, afourth lens group 126 and a diaphragm which is arranged between theelements 123 and 126. For these objectives, the following can beconsidered: an imaging scale β of −0.25±0.15; an image end numericaperture of >0.5; and, an image field diameter >10 mm, preferably >20mm.

The first lens group 121 and the second lens group 123 can be soarranged that the divergence of the rays on the beam splitter surface310 of the polarization beam splitter cube 31 is minimized. If one viewsa peripheral ray which originates from an object point on the opticalaxis, then the sine of the angle of this ray with respect to the opticalaxis can be reduced up to 40% by the first and second lens groups 121and 123. The lens group 124 must have a negative refractive power inorder to obtain an adequate color correction together with the concavemirror 125. The lens group 126 generates the image in the wafer plane 6and therefore exhibits a positive refractive power. The reductionobjective 12, which is shown in FIG. 4, comprises the optical elements121, 122, 123, 124, 125, 126 and the beam splitter cube 31. Thisreduction objective 12 is taken from U.S. Pat. No. 5,880,891incorporated herein by reference.

If one now uses this objective type with a reflective reticle 5, thenthe illuminating light can be coupled in via the polarization beamsplitter cube 31. Advantageously, the fourth unused face of thepolarization beam splitter cube 31 is used for this purpose. It isabsolutely necessary that the illuminating light is polarized more than95% perpendicularly to the beam splitter surface 310 so that noilluminating light is reflected at the beam splitter surface 310 in thedirection of wafer 6 so that thereby contrast and resolution are notreduced. For this reason, it is advantageous to build in a polarizationfilter between illuminating system 2 and polarization beam splitter cube31. The polarization filter has a transmissive polarization directionwhich is orientated perpendicular to the beam splitter surface 310.

A first λ/4 platelet 41 follows the polarization beam splitter cube 31.The light beams of the illuminating beam path 100 are circularlypolarized with the aid of this first λ/4 platelet 41. The light beams ofthe imaging beam path 200 run from the reflective reticle 5 to the wafer6 and are, in turn, linearly polarized by the λ/4 platelet 41 butparallel to the beam splitter surface 310 and are reflected at the beamsplitter surface 310 to the concave mirror 125. Before the light beamsimpinge on the concave mirror 125, the beams are circularly polarized bya second λ/4 platelet 42 and, after the reflection at the concave mirror125 with the second passthrough, are linearly polarized by the secondλ/4 platelet 42 again parallel to the beam splitter layer 310 so thatthe light beams pass through the polarization beam splitter cube 31 inthe direction of wafer 6.

Except for the first λ/4 platelet 41 between polarization beam splittercube 31 and reticle 5, a conventional catadioptric reduction objective12 having a polarization beam splitter cube 31 can be used unchangedwith the reflective reticle 5. What is decisive is that, in the designof the illuminating system 2, the optical elements of the projectionobjective, which are likewise passed through by the illuminating light,also have to be considered.

The light of the light source 1 is so configured in the illuminatingunit 2 that it illuminates the reflective reticle 5 in correspondence tothe lithographic requirements after passing through the following: thepolarization beam splitter cube 31, the first λ/4 platelet 41, thesecond lens group 123, the deflecting mirror 122 and the first lensgroup 121. The homogeneity of the illumination and the illuminating modeis made available by corresponding components in the illuminating system2. The illuminating mode includes coherent, incoherent, annular orquadrupole illumination. In order to correctly illuminate the entrypupil of the reduction objective 12, the polarization beam splitter cube31 and the optical elements 121 to 123 are considered as fixedcomponents of the illuminating beam path 100 and their effect is to beconsidered in the design of the illuminating system 2.

In the configuration of the reduction objective 12 of FIG. 4, it is alsopossible to couple in the illumination light 100 via the deflectionmirror 122 as shown in FIGS. 5 and 6.

In FIG. 5, the deflecting mirror 122 of FIG. 4 is replaced by apolarization beam splitter plate 32. The illuminating light 100 shouldbe so polarized that it passes through the polarization beam splitterplate 32. A λ/4 platelet 43 is disposed between polarization beamsplitter plate 32 and the reticle 5 and leads to the circularpolarization of the illuminating light 100. After the reflection atreticle 5, the light beams of the imaging beam path 200 are polarizedwhen passing through the λ/4 platelet 43 parallel to the beam splittersurface 321 so that the beam is reflected in the direction ofpolarization beam splitter cube 33. The use of a known planes parallelbeam splitter plate, which is positioned in the beam path 200 at anangle of 45°, would lead within the illuminating beam path 100 tonon-rotationally symmetrical imaging errors such as astigmatism and comain the axis. For this reason, the beam splitter plate 32 of theinvention is utilized. This plate is configured as a wedge plate suchthat the astigmatism of lowest order can be completely eliminated by anoptimized wedge angle. The wedge angle is so configured that the thickerend of the wedge is directed toward the illuminating system 2 and thethinner end is directed toward the reticle 5.

The remaining imaging errors of higher order can be compensated by atargeted aspherization of the surface 322 facing toward the illuminatingsystem 2. The aspherization can, for example, be undertaken by an ionbeam or a robotic refinement. The aspheric shape is then, as a rule, notrotationally symmetric; instead, the aspheric form has a simplesymmetry. The symmetry plane is the meridian plane. A correction of thiskind via the wedge plate and the aspherized surface 322 is adequatewithin the illuminating beam path 100 in order to achieve the requiredspecification for the correct illumination of the reticle 5. Incontrast, within the imaging beam path 200, the use of a polarizationbeam splitter plate 32 in transmission would not be possible because ofthe introduced imaging errors. In a configuration of FIG. 5, no adverseeffect on the imaging beam path 200 occurs because, in the imaging beampath 200, only the planar surface 321 of the beam splitter plate 32 isused in reflection so that the light rays of the imaging beam path 200are reflected by air. With air, a medium having a refractive index ofalmost 1.0 is understood. In this connection, consideration can be givenalso to gas fillings, for example, with nitrogen, helium or partiallyevacuated air spaces.

The deflection mirror 122 in FIG. 4 or the beam splitter plate 31 inFIG. 5 can also be replaced by a polarization beam splitter cube 34 asshown in FIG. 6. A polarization beam splitter cube 34 has the advantagecompared to a beam splitter plate 32 that only rotationally symmetricalimaging errors are introduced which can be easily corrected. Incomparison to the beam splitter plate 32, a beam splitter cube 34 hasthe advantage that the additional glass path through the glass prismsleads to transmission losses which are disturbing especially at lowwavelengths.

Coupling in the illuminating light via a polarization beam splitter cube36 can also be done in another class of objective designs as shown inFIG. 7. The reduction objective includes the following: a catadioptriccomponent objective 15 having a polarization beam splitter cube 36, anintermediate image 95 and a refractive reduction objective 16. Thecatadioptric component objective 15 can be disposed after the reticle 5as shown in FIG. 7 as well as forward of the wafer 6. In thecatadioptric component objective 15, a polarization beam splitter cube36 is already provided having a fourth and still unused face. Via thisface, the illuminating light 100 can be coupled in.

The light coming from the illuminating unit 2 has to be very wellpolarized, advantageously to more than 95%, perpendicularly to the beamsplitter surface 360. In this way, one avoids an unwanted reflection inthe direction of wafer 6 whereby contrast and resolution of theprojection objective would have been reduced.

A first λ/4 platelet 47 has to be mounted between polarization beamsplitter cube 36 and reticle 5 so that the light rays of the imagingbeam path 200 are polarized after passing through the λ/4 platelet 47 sothat they are reflected at the polarization beam splitter cube 36 in thedirection of concave mirror 93.

Optical elements 91, which overall have a positive refractive power, aredisposed between reticle 5 and polarization beam splitter cube 36 sothat the beam splitter surface 360 is passed through in the almostentirely collimated beam path.

A second λ/4 platelet 48 has to be introduced between polarization beamsplitter cube 36 and concave mirror 93 so that the light rays of theimaging beam path 200 can, after the deflection at concave mirror 93,pass through the polarization beam splitter cube 36 undeflected in thedirection of the intermediate image 95.

The optical elements 92 having an overall negative refractive power aredisposed between the polarization beam splitter cube 36 and the concavemirror 93. The elements 92 are passed through by the light beam in twopassthroughs and lead to a chromatic overcorrection. The concave mirror93 affords the advantage that it introduces no chromatic aberrations andhas an adequately positive refractive power so that the catadioptriccomponent objective 15 overall has a positive refractive power.

If the polarization beam splitter cube 3 is passed through in the almostcollimated beam path, then further optical elements 94 having overallpositive refractive power are required ahead of the intermediate image95 in order to generate the intermediate image.

One can omit optical elements 94 if the intermediate image 95 is alreadygenerated by the action of the concave mirror 93 and the opticalelements 92 and if the collimated beam path within the polarization beamsplitter cube 93 is omitted.

Usually, the object is imaged onto the intermediate image with animaging scale of β₁=−1.0±0.25.

A refractive reduction imaging having an imaging scale of, for example,β₂=0.25±0.15 follows the intermediate image 95. In FIG. 7, the componentobjective between intermediate image 95 and wafer 6 comprises theoptical elements (96, 98) and the deflecting mirror 97.

It is also possible to arrange the deflecting mirror 97 forward of theoptical components 96.

The diameter of the illuminated field in the wafer plane 6 is, in thisclass of objectives, greater than 10 mm for an image end numericalaperture greater than 0.5.

For the embodiment shown in FIG. 7 with beam splitter cube andintermediate image, FIG. 8 shows a specific embodiment for an imagescale β=−0.25, for an image field having a diameter of 14.3 mm and foran image end numerical aperture of 0.7. The reference numerals in FIG. 8correspond to the reference numerals in FIG. 7. The optical data are setforth in Table 1.

The embodiment of FIG. 8 is taken from U.S. patent application Ser. No.09/711,256, filed Nov. 10, 2000 (now U.S. Pat. No. 6,424,471),incorporated herein by reference.

In Table 1, the surface 7 is assigned to the beam splitter surface 360for the first contact and the surface 19 is assigned to the concavemirror 93. The surface 31 is assigned to the beam splitter surface 360for the second contact and the surface 36 is assigned to the deflectingmirror 97. The surface 38 is assigned to the intermediate image 95. SiO₂identifies quartz glass and CaF₂ identifies calcium fluoridemonocrystals.

The optical elements 91 in this case comprise two converging lenses 131and 132. The converging lens 132 is mounted close to the polarizationbeam splitter cube 3 and reduces the divergence of the peripheral rays.In this way, the substantially collimated beam path is produced withinthe polarization beam splitter cube 3. An almost telecentric chief raytrace is achieved at the reticle 5 with the converging lens 131 close tothe reticle 5.

Table 2 provides the chief ray angles with respect to the surface normalin mrad for seven object heights in the reticle plane 5. The chief rayangles are positive when the chief rays run convergent to the opticalaxis after reflection at reticle 5. The maximum chief ray angle in thisembodiment is only 0.5 mrad. The entry at the reticle is thereby almostperfectly telecentric.

The adaptation of the centroid ray angles of the illuminating beam path100 in the illuminating system 2 to the chief ray angle of theprojection objective is, in this case, especially simple because theilluminating beam path 100 and the imaging beam path 200 substantiallyoverlap within the common components 91 between beam splitter cube 3 andreticle 5.

The polarization beam splitter cube 3 and the two converging lenses 131and 132 are to be included in the design of the illuminating system 2.If the last component of the illuminating system 2 forward of thereticle is a REMA objective as disclosed in U.S. Pat. No. 5,982,558 orin U.S. Pat. No. 6,366,410, then the REMA objective can be so modifiedwithout great difficulty that a refractive cube is integrated for thepolarization beam splitter cube 3 and a refractive planar plate isintegrated for the λ/4 platelet 47 and the two converging lenses 131 and132 are integrated into the field lens of the REMA objective.

An incoupling of the illuminating light 100 via the deflecting mirror 97is in this case not possible. The incoupling of illuminating light via apolarization beam splitter cube or a polarization beam splitter plate isonly possible when the light does not impinge on a further beam splittersurface after passing through this first beam splitter surface but isreflected after passthrough by possibly further optical elements.However, in the configuration of FIG. 8, if the illuminating light wouldbe coupled in via the deflecting mirror 97, no reflecting surface wouldfollow but a further polarization beam splitter surface 360 of the beamsplitter cube 3. An incoupling would, in this case, be conceivable onlyvia a geometric beam splitter plate or a geometric beam splitter cube.This, however, would lead to high transmission losses.

It is understood that the foregoing description is that of the preferredembodiments of the invention and that various changes and modificationsmay be made thereto without departing from the spirit and scope of theinvention as defined in the appended claims.

TABLE 1 Surface No. Radius Thickness Mirror Material Reticle ∞ 35.000  1∞ 0.000  2 ∞ 10.000 SiO2  3 −356.062 157.474  4 152.317 20.000 SiO2  5−207.509 15.494  6 ∞ 46.000 SiO2  7 ∞ −46.000 S SiO2  8 ∞ −11.450  9714.294 −10.000 SiO2 10 −233.153 −14.054 11 11257.823 −7.320 SiO2 125681.927 −0.268 13 −294.458 −29.996 SiO2 14 2624.912 −21.086 15 118.550−6.001 SiO2 16 372.661 −9.646 17 89.532 −6.000 SiO2 18 220.679 −3.804 19134.415 3.804 S 20 220.679 6.000 SiO2 21 89.532 9.646 22 372.661 6.001SiO2 23 118.550 21.086 24 2624.912 29.996 SiO2 25 −294.458 0.268 265681.927 7.320 SiO2 27 11257.823 14.054 28 −233.153 10.000 SiO2 29714.294 11.450 30 ∞ 46.000 SiO2 31 ∞ 46.000 SiO2 32 ∞ 0.000 33 ∞ 11.00034 −6197.721 20.000 SiO2 35 −220.469 289.683 36 ∞ −35.000 S 37 −283.115−27.145 SiO2 38 291.549 −0.100 39 −169.090 −12.856 SiO2 40 −2565.582−24.512 41 380.926 −6.000 SiO2 42 3955.807 −18.476 43 360.725 −6.000SiO2 44 890.059 −2.724 45 −179.574 −11.560 SiO2 46 −339.907 −16.696 47−147.863 −16.313 SiO2 48 −65.738 −18.352 49 103.683 −7.718 SiO2 50197.447 −2.785 51 111.947 −15.000 SiO2 52 106.337 −38.908 53 −152.812−22.411 SiO2 54 194.070 −0.375 55 −199.667 −7.318 SiO2 56 −93.343−30.485 57 89.838 −7.125 SiO2 58 197.820 −35.859 59 −713.001 −13.228SiO2 60 274.158 −0.375 61 −106.260 −6.375 SiO2 62 −76.991 −18.206 63−207.243 −16.125 SiO2 64 265.977 −0.375 65 −105.982 −6.938 SiO2 66−70.150 −5.070 67 −110.355 −11.250 SiO2 68 −337.355 −1.500 69 ∞ 0.000 70−83.054 −13.500 SiO2 71 −64.019 −0.100 72 −60.890 −13.500 SiO2 73−102.440 −0.101 74 −65.466 −8.393 SiO2 75 −75.287 −0.523 76 −74.115−10.249 SiO2 77 −48.411 −4.972 78 −70.661 −26.250 SiO2 79 135.365 −0.03880 −38.281 −23.828 CaF2 81 −41.066 −0.038 82 −46.927 −9.292 CaF2 83187.500 −5.625 Wafer ∞ 0.000

TABLE 2 Object Height at Reticle Chief Ray Angle at Reticle (mm) (mrad)28.7 +0.29 26.8 +0.36 24.9 +0.41 20.3 +0.49 14.4 +0.47 10.1 +0.38 0.0+0.00

1. A projection exposure system for microlithography, the projectionexposure system comprising: a light source; an illuminating systemmounted downstream of said light source for transmitting light from saidlight source as an illuminating beam along an illuminating beam path; areflective reticle; a reduction objective defining an imaging beam pathand being configured for imaging said reticle onto an object; a beamsplitter cube mounted in said imaging beam path for mutually superposingsaid illuminating beam path and said imaging beam path; optical elementsmounted on said imaging beam path between said reflective reticle andsaid beam splitter cube; and, said illuminating light beam having chiefrays which impinge on said reflective reticle at an angle of incidencehaving a value up to |15| mrad.
 2. The projection exposure system ofclaim 1, wherein said angle of incidence is up to |5| mrad.
 3. Theprojection exposure system of claim 1, wherein said angle of incidenceis up to |1.0| mrad.
 4. The projection exposure system of claim 1,wherein said illuminating light beam has centroidal rays which, afterbeing reflected at said reflective reticle, deviate from said chief raysby a maximum of |2.5| mrad.
 5. A projection exposure system formicrolithography, the projection exposure system comprising: a lightsource; an illuminating system mounted downstream of said light sourcefor transmitting light from said light source as an illuminating beamalong an illuminating beam path; a reflective reticle; a reductionobjective defining an imaging beam path and being configured for imagingsaid reticle onto an object; a beam splitter cube mounted in saidimaging beam path for mutually superposing said illuminating beam pathand said imaging beam path; said beam splitter cube being a polarizationbeam splitter cube having a beam splitter surface; and, the light ofsaid illuminating light beam, before entering said polarized beamsplitter cube, being linearly polarized to more than 95% perpendicularto said beam splitter surface when said illuminating beam is not to bereflected at said beam splitter surface or being linearly polarized tomore than 95% parallel to said beam splitter surface when theilluminating beam path is to be reflected at said beam splitter surface.6. The projection exposure system of claim 5, wherein said reductionobjective is a catadioptric objective.
 7. The projection exposure systemof claim 6, wherein said beam splitter cube is a first beam splittercube; said reduction objective includes a concave mirror and a secondbeam splitter cube which separates the beam path to and from saidconcave mirror.
 8. The projection exposure system of claim 6, whereinsaid first beam splitter cube defines a deflecting surface in the beampath of said reduction objective.
 9. The projection exposure system ofclaim 8, wherein said reduction objective is configured to be free of anintermediate image.
 10. The projection exposure system of claim 8,wherein said reduction objective is configured to have an intermediateimage.
 11. A projection exposure system for microlithography, theprojection exposure system comprising: a light source; an illuminatingsystem mounted downstream of said light source for transmitting lightfrom said light source as an illuminating beam along an illuminatingbeam path; a reflective reticle; a reduction objective defining animaging beam path and being configured for imaging said reticle onto anobject; a beam splitter cube mounted in said imaging beam path formutually superposing said illuminating beam path and said imaging beampath; said reduction objective including a first objective incorporatingsaid beam splitter, an intermediate image; and, a second objective; and,said first objective having an imaging scale of −1.0±0.25 and saidsecond objective having an intermediate imaging scale of −0.25±0.15. 12.The projection exposure system of claim 11, wherein said first objectiveand said second objective are configured to be purely refractive. 13.The projection exposure system of claim 11, wherein said first objectiveis configured to be purely refractive; and, said second objective isconfigured to be catadioptric.
 14. A projection exposure system formicrolithography, the projection exposure system comprising: a lightsource; an illuminating system mounted downstream of said light sourcefor transmitting light from said light source as an illuminating beamalong an illuminating beam path; a reflective reticle; a reductionobjective defining an imaging beam path and being configured for imagingsaid reticle onto an object; a beam splitter plate for mutuallysuperposing said illuminating beam path and said imaging beam path; saidbeam splitter plate having a first surface on which said imaging beampath is reflected in air and said beam splitter plate having a secondsurface; and, said first surface being a planar surface and said secondsurface being a corrective surface deviating from said planar surface.15. The projection exposure system of claim 14, wherein said beamsplitter plate is wedge shaped.
 16. The projection exposure system ofclaim 14, wherein said illuminating beam is refractively corrected inpassing through said beam splitter plate.
 17. The projection exposuresystem of claim 16, wherein said beam splitter plate defines adeflecting surface in the beam path of said reduction objective.
 18. Theprojection exposure system of claim 15, wherein only refractive elementsand a λ/4 platelet are provided between said beam splitter plate andsaid reflective reticle.
 19. The projection exposure system of claim 15,wherein said beam splitter plate is accommodated in a catadioptricreduction objective.
 20. The projection exposure system of claim 19,wherein said catadioptric reduction objective is configured to be freeof an intermediate image.
 21. A method for making a microstructuredobject with a projection exposure system for microlithography whichincludes: a light source; a reflective reticle defining a reticle plane;an illuminating system mounted downstream of said light source fortransmitting light from said light source along an illuminating beampath as an illuminating light beam having chief rays which impinge onsaid reflective reticle at an angle of incidence having a value up to|15| mrad; a reduction objective defining an imaging beam path and animaging plane and being configured for imaging said reticle onto theobject; and, a beam splitter cube mounted in said imaging beam path formutually superposing said illuminating beam path and said imaging beampath; and, the method comprising the steps of: placing an object in theform of a substrate having a light-sensitive layer in said imagingplane; inserting a mask containing a pattern thereon into saidilluminating beam path at said reticle plane; imaging said pattern ontosaid lightsensitive light-sensitive layer of said substrate utilizingsaid projection exposure system; and, exposing said light-sensitivelayer by passing the light of said light source along said illuminatingbeam path thereby structuring said substrate.
 22. A method for making amcirostructured object with a projection exposure system formicrolithography which includes: a light source; an illuminating systemmounted downstream of said light source for transmitting light from saidlight source as an illuminating beam along an illuminating beam path; areflective reticle defining a reticle plane; a reduction objectivedefining an imaging beam path and an imaging plane and being configuredfor imaging said reticle onto an object; a beam splitter plate formutually superposing said illuminating beam path and said imaging beampath; said beam splitter plate having a first surface on which saidimaging beam path is reflected in air and said beam splitter platehaving a second surface; and, said first surface being a planar surfaceand said second surface being a corrective surface deviating from saidplanar surface; and, the method comprising the steps of: placing anobject in the form of a substrate having a light-sensitive layer in saidimaging plane; inserting a mask containing a pattern thereon into saidilluminating beam path at said reticle plane; imaging said pattern ontosaid light-sensitive layer of said substrate utilizing said projectionexposure system; and, exposing said light-sensitive layer by passing thelight of said light source along said illuminating beam path therebystructuring said substrate.
 23. A projection exposure system formicrolithography, the projection exposure system comprising: a lightsource; an illuminating system mounted downstream of said light sourcefor transmitting light from said light source as an illuminating beamalong an illuminating beam path; a reflective reticle; a reductionobjective defining an imaging beam path and being configured for imagingsaid reticle onto an object; a beam splitter cube mounted in saidimaging beam path for mutually superposing said illuminating beam pathand said imaging beam path; said reduction objective being acatadioptric objective; said beam splitter cube being a first beamsplitter cube; and, said reduction objective including a concave mirrorand a second beam splitter cube which separates the beam path to andfrom said concave mirror.
 24. A microlithographic projection exposuresystem comprising: a light source; an illuminating system; a reticle;and a reduction objective being configured for imaging said reticle ontoan object, wherein said reduction objective includes: a first objective;an intermediate image; a second objective comprising a concave mirror; asecond intermediate image; a third objective in sequence; and adeflecting mirror with two deflecting surfaces.
 25. The system of claim24, wherein said first objective has an imaging scale of one of thegroup consisting of −1.0±0.25 and −0.5±0.2.
 26. A microlithographicprojection exposure system comprising: a light source; an illuminatingsystem; a reticle; and a reduction objective being configured forimaging said reticle onto an object, wherein said reduction objectiveincludes: a first objective; an intermediate image; a second objectivecomprising a concave mirror; a second intermediate image; a thirdobjective in sequence; and a deflecting mirror with two deflectingsurfaces; wherein the reduction objective has an image end numericalaperture of a value of more than 0.8.
 27. A projection exposure systemfor microlithography for imaging a reticle to a wafer plane with twointermediate image planes comprising: a first intermediate imagingsystem for imaging of a reticle to a first intermediate image; and acatadioptric intermediate imaging system having an object field; whereinthe object field of the catadioptric intermediate imaging system isdecentered with respect to the optical axis, and having a deflectingmirror with two deflecting surfaces.
 28. A system according to claim 27,wherein said catadioptric intermediate imaging system is arranged offsetto the first intermediate imaging system.
 29. A system according toclaim 27, wherein said first intermediate imaging system has an imagingscale of one of the group consisting of −1.0±0.25 and −0.5±0.2.
 30. Asystem according to claim 27, wherein said catadioptric intermediateimaging system comprises a concave mirror.
 31. A system of claim 27,wherein the reduction objective has an image end numerical aperture of avalue of more than 0.8.
 32. A microlithographic projection exposuresystem comprising: a light source; an illuminating system; a reticle;and a reduction objective being configured for imaging said reticle ontoan object; wherein said reduction objective includes: a first objectiveproviding an intermediate image; a catadioptric objective comprising aconcave mirror; a second intermediate image; a purely refractiveobjective; and a wafer plane parallel to said reticle.
 33. The system ofclaim 32, wherein said first objective has an imaging scale of one ofthe group consisting of −1.0±0.25 and −0.5±0.2.
 34. A system of claim32, wherein the reduction objective has an image end numerical apertureof a value of more than 0.8.
 35. A projection exposure system formicrolithography for imaging a reticle to a wafer plane with twointermediate image planes comprising: a first intermediate imagingsystem for imaging of the reticle to a first intermediate image; acatadioptric intermediate imaging system for imaging the firstintermediate image to a second intermediate image; wherein the objectfield of the catadioptric intermediate imaging system is not centeredwith respect to the optical axis, said wafer plane being parallel tosaid reticle.
 36. A system according to claim 35, wherein saidcatadioptric intermediate imaging system is arranged offset to the firstintermediate imaging system.
 37. A system according to claim 35, whereinsaid first intermediate imaging system has an imaging scale of one ofthe group consisting of −1.0±0.25 and −0.5±0.2.
 38. A system accordingto claim 35, wherein said catadioptric intermediate imaging systemcomprises a concave mirror and a deflecting mirror with two deflectingsurfaces.
 39. A system according to claim 32, further comprising adeflecting mirror with two deflecting surfaces.
 40. The system of claim26, wherein said first objective has an imaging scale of one of thegroup consisting of −1.0±0.25 and −0.5±0.2.